Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 AM EST Fri Jan 17 2020

Valid 12Z Fri Jan 17 2020 - 12Z Mon Jan 20 2020


Day 1...

...Midwest...
Strong isentropic lift and low level warm air advection ahead of
an upper level shortwave will support precipitation spreading
northeast from the central Plains and mid Mississippi valley into
the Upper Midwest on Friday. 

As the air column moistens, the very dry, low level air that is
currently in place will support a period of snow and/or sleet
across the Ozarks and mid Mississippi valley early Friday before
changing over to freezing rain as the column aloft continues to
warm.  Significant ice accumulations are possible across the
region before precipitation changes over rain during the evening
and overnight hours.  WPC PWPF indicates that ice accumulations of
0.10-0.25 inch are likely across a large portion of Missouri into
western Illinois.

Snow is forecast to remain the primary precipitation type farther
to the north.  Although the overnight guidance has backed off some
on amounts, heaviest totals are still expected to center from the
Iowa-Minnesota border into central Minnesota.  A prolonged period
of southeasterly flow will also contribute to locally heavy, lake
enhanced amounts north of Lake Superior into the Arrowhead region.
 WPC PWPF shows high probabilities for snow accumulations of 6
inches or greater across these areas.

Day 2...

...Great Lakes/Northeast/Northern Mid Atlantic...
Low pressure lifting into the Upper Great Lakes on Saturday is
forecast to slide east into the St Lawrence Valley Saturday night
as a second low begins to develop along the northern New England
coast.  In the warm advection pattern ahead of the low, models are
in good agreement --indicating light to moderate snows spreading
east across Upstate New York and New England, with a wintry mix
changing to rain farther south.  By Saturday night, low pressure
developing along the northern New England coast may contribute to
additional amounts across portions of New Hampshire and Maine
before moving south of Nova Scotia Sunday morning. 

In addition to the synoptic snows, westerly winds will support a
prolonged period of lake enhancement that will begin Saturday
night and continue into Sunday, with heavy snow totals likely east
of Lake Ontario through the Tug Hill region.  WPC PWPF indicates a
strong potential for locally heavy amounts of a foot or more
across this region. 

Meanwhile, westerly winds will also support locally heavy totals
east of Lake Erie, while northwesterly winds will produce locally
heavy amounts across portions of northern Michigan.

...Northwest...
A warm front lifting north across the region will support high
elevation snow, with heavy amounts possible across portions of the
Olympics and northern Cascades.

Day 3...

...Great Lakes...
Lake effect snow showers will continue into Sunday, with
additional heavy accumulations possible, especially east of the
Lower Lakes, before winds become more northerly across the lakes
Sunday night.

The probability of significant icing (0.25 inch or greater) is
less than 10 percent.

Pereira